Broadcom RAID Boards Support Distributed Sparing
Instead of using a dedicated drive for hot-swapping, Broadcom Corp.s enhanced RAIDCore Serial ATA controller pulls the mirrored data off the failing drive and allocates it across the remaining good disks. According to Irvine, Calif.-based Broadcom, this will allow IT managers to forgo a dedicated hot-swap disk.
The additional enhancements are designed to bring peace of mind to a systems administrator, who always has to worry about a drive failing and the corresponding data loss.
In a typical RAID 5 array, a dedicated "hot spare" disk is used to replace a drive that has failed, with the data on the failed drive mirrored on another in the array.
But Broadcoms argument is that the hot spare can sit idle and itself quietly fail, leaving the system without a safety net.
Instead, the RAIDCore adapters will use unused space on the other drives on the array to store the data from a failed drive until a fresh replacement can be added.
Although the controller is being positioned as a cost-saving alternative, IT managers also can use the RAIDCore chips as an additional layer of redundancy, allowing the system to fail over to the hot spare and then to the rest of the array, or vice versa.
The length of time needed to propagate the mirrored data to the rest of the array will be about the same as the time needed to mirror data to the backup disk, Steve McIntosh, a RAIDCore product manager, said in an interview.
Distributed sparing has been a topic of academic papers within the storage industry dating back at least to 1997. Enterprise storage companies such as Hewlett-Packard Co., meanwhile, have developed applications such as the HP StorageWorks Continuous Access EVA to handle distributed sparing.
The new RAIDCore controllers also support online capacity expansion, online RAID-level migration, controller spanning and the ability to create arrays that span multiple controllers, all without having to bring the system down.
All are features common in higher-end SCSI HBAs, but online capacity expansion and RAID-level migration are firsts for Serial ATA controllers, he said.
The additional features come courtesy of Broadcoms XelCore RAID software stack and Fulcrum architecture, which was acquired in January as part of the companys acquisition of RAIDCore Inc.
Correction: The RaidCore line will be sold as boards.